Visual C++ Classes in Class Designer

Class Designer supports C++ classes and visualizes native C++ classes in the same way as Visual Basic and Visual C# class shapes, except that C++ classes can have multiple inheritance relationships. You can expand the class shape to show more fields and methods in the class or collapse it to conserve space.

Note

Class Designer does not support unions (a special type of class in which the memory allocated is only the amount necessary for the union's largest data member).

Simple Inheritance

When you drag more than one class onto a class diagram, and the classes have a class inheritance relationship, an arrow connects them. The arrow points in the direction of the base class. For example, when the following classes are displayed in a class diagram, an arrow connects them, pointing from B to A:

class A {};
class B : A {};

You can also drag only class B to the class diagram, right-click the class shape for B, and then click Show Base Classes. This displays its base class: A.

Multiple Inheritance

Class Designer supports the visualization of multiple-class inheritance relationships. Multiple inheritance is used when a derived class has attributes of more than one base class. Following is an example of multiple inheritance:

class Bird {};
class Swimmer {};
class Penguin : public Bird, public Swimmer {};

When you drag more than one class onto the class diagram, and the classes have a multiple-class inheritance relationship, an arrow connects them. The arrow points in the direction of the base classes.

Right-clicking a class shape and then clicking Show Base Classes displays the base classes for the selected class.

Note

The Show Derived Classes command is not supported for C++ code. You can display derived classes by going to Class View, expanding the type node, expanding the Derived Types subfolder, and then dragging those types onto the class diagram.

For more information about multiple-class inheritance, see Multiple Inheritance and Multiple Base Classes.

Abstract Classes

Class Designer supports abstract classes (also named "abstract base classes"). These are classes that you never instantiate, but from which you can derive other classes. Using an example from "Multiple Inheritance" earlier in this document, you might instantiate the Bird class as individual objects as follows:

int main()
{
   Bird sparrow;
   Bird crow;
   Bird eagle;
}

However, you might not intend to instantiate the Swimmer class as individual objects. You might intend only to derive other types of animal classes from it, for example, Penguin, Whale, and Fish. In that case, you would declare the Swimmer class as an abstract base class.

To declare a class as abstract, you can use the abstract keyword. Members marked as abstract, or included in an abstract class, are virtual and must be implemented by classes that derive from the abstract class.

class Swimmer abstract
{
   virtual void swim();
   void dive();
};

You can also declare a class as abstract by including at least one pure virtual function:

class Swimmer
{
   virtual void swim() = 0;
   void dive();
};

When you display these declarations in a Class Diagram, the class name Swimmer and its pure virtual function swim are in displayed in italic in an abstract class shape, together with the notation Abstract Class. Notice that the abstract class type shape is the same as that of a regular class, except that its border is a dotted line.

A class derived from an abstract base class must override each pure virtual function in the base class, or the derived class cannot be instantiated. So, for example, if you derive a Fish class from the Swimmer class, Fish must override the swim method:

class Fish : public Swimmer
{
   void swim(int speed);
};

int main()
{
   Fish guppy;
}

When you display this code in a Class Diagram, Class Designer draws an inheritance line from Fish to Swimmer.

Anonymous Classes

Class Designer supports anonymous classes. Anonymous class types are classes declared without an identifier. They cannot have a constructor or destructor, cannot be passed as arguments to functions, and cannot be returned as return values from functions. You can use an anonymous class to replace a class name with a typedef name, as in the following example:

typedef struct
{
    unsigned x;
    unsigned y;
} POINT;

Structures can also be anonymous. Class Designer displays anonymous classes and structures the same as it displays the respective type. Although you can declare and display anonymous classes and structures, Class Designer will not use the tag name that you specify. It will use the name that Class View generates. The class or structure appears in Class View and Class Designer as an element called __unnamed.

For more information about anonymous classes, see Anonymous Class Types.

Template Classes

Class Designer supports the visualization of template classes. Nested declarations are supported. The following table shows some typical declarations.

Code element	Class Designer view
template <class T> class A {};	A<T> Template Class
template <class T, class U> class A {};	A<T, U> Template Class
template <class T, int i> class A {};	A<T, i> Template Class
template <class T, template <class K> class U> class A {};	A<T, U> Template Class

The following table shows some examples of partial specialization.

Code element	Class Designer view
template<class T, class U> class A {};	A<T, U> Template Class
template<class T> class A<T, T> {};	A<T, T> Template Class
template <class T> class A<T, int> {};	A<T, int> Template Class
template <class T1, class T2> class A<T1*, T2*> {};	A<T1*, T2*> Template Class

The following table shows some examples of inheritance in partial specialization.

Code element	Class Designer view
template <class T, class U> class A {}; template <class TC> class A<T, int> {}; class B : A<int, float> {}; class C : A<int, int> {};	A<T, U> Template Class B Class (points to Class A) C Class (points to Class A)

The following table shows some examples of partial specialization template functions.

Code element	Class Designer view
class A { template <class T, class U> void func(T a, U b); template <class T> void func(T a, int b); };	A func<T, U> (+ 1 overload)
template <class T1> class A { template <class T2> class B {}; }; template<> template<> class A<type>::B<type> {};	A<T1> Template Class B<T2> Template Class (B is contained within class A under Nested Types)
template <class T> class C {}; class A : C<int> {};	A Class -> C<int> C<T> Template Class

The following table shows some examples of template inheritance.

Code element	Class Designer view
template <class T> class C {}; template<> class C<int> { class B {}; } class A : C<int>::B {};	A Class ->B C<int> Class (B is contained within class C under Nested Types) C<T> Template Class

The following table shows some examples of canonical specialized class connection.

Code element	Class Designer view
template <class T> class C {}; template<> class C<int> {}; class A : C<int> {}; class D : C<float> {};	A Class ->C<int> C<int> Class C<T> Template Class D Class ->C<float>
class B { template <class T> T min (const T &a, const T &b); };	B min <T>

See Also

Reference

Classes, Structures, and Unions

Anonymous Class Types

Multiple Inheritance

Multiple Base Classes

Concepts

Working with Visual C++ Code (Class Designer)

Other Resources

Templates